1. Technical Field
The present invention relates to liquid ejecting apparatuses as exemplified by facsimile devices, printers, or the like.
2. Related Art
The following describes an ink jet printer as an example of a liquid ejecting apparatus. An ink jet printer has a support member (also called a platen) in a location that is opposite to an ink jet recording head, and is configured so that the distance between the ink jet recording head and the recording paper is defined by supporting the recording paper using the support member.
In recent ink jet printers, a trend toward smaller ink droplets is progressing with the aim of further improving the quality of recording, and ink droplets have been reduced in size to, for example, approximately several pls each. For this reason, the mass of the ink droplets is extremely low, and thus when ink droplets are ejected from the ink jet recording head onto the recording paper, some of the ink droplets turn into mist and float rather than landing upon the recording paper, which has caused a variety of problems. In addition, in so-called “borderless recording”, in which recording is carried out without leaving margins on the four sides of the recording paper, the aforementioned floating mist phenomenon is even more evident due to ink droplets being ejected into regions that are outside of the edges of the recording paper.
Accordingly, techniques have been proposed in the past in which potential differences are applied between the ink jet recording head, the recording paper, and the support member, instigating Coulomb force on the ink droplets by generating an electrical field, thus pulling the ink droplets back toward the recording paper, as disclosed in JP-A-2007-118321 and JP-A-2007-118318.
Meanwhile, increases in speeds are advancing in recent ink jet printers, particularly in business applications, and thus the speed at which paper is transported has increased significantly as compared to the past. Furthermore, in so-called serial type ink jet printers, in which recording is carried out while the ink jet recording head moves in the direction that is perpendicular to the paper transport direction, head scans (recording) are executed while the paper is stopped, and thus it is necessary to further increase the paper transport speed in order to prevent a drop in throughput.
In addition, recent ink jet printers capable of executing recording with extremely high throughput using what is known as a line head, or a fixed-type ink jet recording head that does not perform scans (that is, does not move), have been proposed. With such ink jet printers, the recording paper is transported along a paper transport path within the apparatus at an extremely high speed.
However, it has been discovered that the following problems arise due to such an increase in the transport speed of the recording paper. First, paper particles produced when cutting the paper adhere to the edges of the recording paper, and in the case where the potential between the three elements of the recording paper, the support member (platen), and the ink jet recording head (collectively called the “recording unit constituent elements” hereinafter) is not controlled, the paper particles that had been adhering to the recording paper fly toward the ink jet recording head and adhere thereto due to the electrical field that has arisen between the recording unit constituent elements. This flight of paper particles is even more apparent in the case where the recording paper is transported at a high speed because vibrations, shocks of collisions, and so on that occur during the paper transport are more pronounced.
In addition, frictional electrification, separation electrification, and the like become apparent due to friction between pieces of recording paper that are held in a paper cassette, sliding/contact between the constituent elements of the paper transport path (for example, edge guides, transport rollers, or the like) and the recording paper, which results in the recording unit constituent elements being charged to a higher degree. As a result, the electrical field that is formed between the recording unit constituent elements grows stronger and the charge of the paper particles itself is also strengthened, and due to this, the Coulomb force that acts on the paper particles grows, causing the adherence of the paper particles to the ink jet recording head to become even more pronounced.
Meanwhile, even in the case where the paper particles themselves are not charged, if the paper particles that have flown are located within the electrical field, an electrical charge bias will occur in the paper particles due to induced polarization or electrostatic induction, which will pull the paper particles toward the ink jet recording head.
FIG. 7 is a descriptive diagram illustrating this problematic point, where the numeral 160 indicates an ink jet recording head, the numeral 160a indicates a nozzle plate, the numeral 170 indicates a support member (platen), and the numerals 170a indicate ribs formed in the support member 170. In addition, the letter P indicates recording paper, the letters Pe indicate an edge of the paper, and the letter d indicates paper particles. Furthermore, the “plus” and “minus” signs in circles indicate charge polarities.
The recording paper P is de-electrified by a de-electrifying brush or the like, and thus the paper particles d that adhere to the recording paper P are not charged. However, as shown in the enlargement diagram in FIG. 7 that illustrates the paper particles d, in the (exemplary) case where the nozzle plate 160a is positively charged and the support member 170 is negatively charged, a negative charge appears on the nozzle plate side of the paper particles d and a positive charge appears on the support member side of the paper particles d due to the induced polarization (in the case where the paper particles d have dielectric properties) or the electrostatic induction (in the case where the paper particles d have conductive properties). Accordingly, the paper particles d are pulled toward either the nozzle plate 160a or the support member 170.
Paper particles d adhering to the ink jet recording head 160 can lead to missing dots due to the paper particles d directly obstructing the nozzle openings or due to paper particles d moving into the nozzle openings when the nozzle surface are cleaned (wiped).
In addition to the paper particles physically obstructing the nozzle openings in this manner, there are also cases where filler such as calcium carbonate that is contained in the paper particles reacts with the moisture in the ink and causes thickening, which inhibits vibrations in the meniscuses at the nozzle openings and interferes with the ejection of ink droplets. Accordingly, preventing paper particles from adhering to the ink jet recording head is extremely important in order to obtain a suitable recording quality in an ink jet printer.
The aforementioned JP-A-2007-118321 and JP-A-2007-118318 propose techniques in which, as described earlier, potential differences are applied between the ink jet recording head, the recording paper, and the support member (the recording unit constituent elements), instigating Coulomb force on the ink droplets by generating an electrical field and pulling the ink droplets back toward the recording paper. Accordingly, if the paper particles are considered physically same as the ink droplets, it is thought that controlling the electrical field pulls the paper particles toward the recording paper, which will make it possible to prevent the paper particles from adhering to the ink jet recording head.
However, the cellulose fibers and filling materials of which the paper particles are composed are easily charged to either positive or negative polarities in terms of triboelectric series, and thus even if the paper particles are prevented from flying toward the ink jet recording head by forming an electrical field in a specific direction between the recording unit constituent elements, it is not possible to prevent the paper particles that have been charged to the opposite polarity from flying toward the ink jet recording head.
It should be noted that JP-A-2003-165230 discloses a recording apparatus configured so that air ducts are provided in the periphery of a nozzle plate and humidified air is ejected from the air ducts during recording and when standing by for recording as one way of preventing paper particles, dust, and the like from adhering to the vicinity of a nozzle unit in an ink jet recording head. However, with such a configuration, the complexity of the configuration leads to a larger apparatus size and an increase in costs, and there is also the risk that the airflow itself will cause paper particles to adhere to the recording head.